1. Field of the Invention
The present invention relates to a battery charge control device which has a "gassing" deciding function to detect an occurrence of the gassing state caused in a battery on a vehicle at the vehicle's traveling, without using a temperature sensor and with ease and accuracy.
2. Description of Related Art
Under general condition that the battery is being charged, if its terminal voltage exceeds a stated voltage, then the battery begins to generate gas (e.g. oxygen gas, hydrogen gas) due to the electrolysis of water contained in the battery. Note that the terminal voltage at the time of beginning to generate such the gas is normally referred to as "gassing voltage". As the function of temperature of the electrolyte (liquid) in the battery, the gassing voltage Vgs can be obtained by the following formula of: EQU Vgs=.alpha.-.beta.(T-20.degree. C.) (1)
wherein .alpha., .beta. are the battery's intrinsic constants; and
T is the temperature of the electrolyte.
Especially in the "hybrid" vehicle equipped with a plurality of power sources, such as an engine and an alternator, a great deal of regenerative energy (electric power) during the vehicle's traveling is charged into the battery one after another. Under the situation, it is remarkably important to detect whether or when the terminal voltage of the battery is reaching the above gassing voltage Vgs in view of preventing the deterioration of battery.
In order to acknowledge the terminal voltage's reaching the gassing voltage Vgs, for example, there is a known system where the battery is equipped with the temperature sensor.
In this system employing the temperature sensor in order to detect the reach for the gassing voltage Vgs, it is executed to calculate it on the basis of a temperature informed by the temperature sensor, in accordance with the above formula (1). Also in the system, when the terminal voltage of the battery reaches the gassing voltage Vgs, it is executed to switch the present charging current into a new charging current prepared for the next stage (i.e. a new current smaller than the current) in view of restricting the generation of gas in the electrolyte.
In the above-mentioned system, however, there exists a problem that the embodied apparatus is high-priced because of the installation of the temperature sensor. Additionally, in order to calculate the gassing voltage Vgs as the function of temperature, the calculation program installed on the apparatus is complicated.
Note that it is desirable to position the temperature sensor in the electrolyte (liquid) in view of detecting the temperature of the electrolyte in the battery precisely. Nevertheless, in the present circumstances, it is impossible to dip the temperature sensor in the electrolyte.
Since, in actuality, the temperature sensor is arranged in the vicinity of the battery or pasted on a sidewall of the battery, there is a difference between the actual temperature of the electrolyte and the temperature information provided by the temperature sensor.
Additionally, it is unavoidable that the temperature of air outside affects the so-positioned temperature sensor.
Thus, the gassing voltage Vgs based on the temperature information provided by the temperature sensor has a reduced reliability in its accuracy due to the above difference between the actual temperature of the electrolyte and the temperature detected by the temperature sensor.
In summary, the conventional system has drawbacks that the gassing cannot be detected despite that the terminal voltage of the battery has already reached the gassing voltage during the vehicle's traveling, and vice versa (erroneous detection of the gassing despite that the battery voltage has not reach the gassing voltage yet). Such the drawbacks cause either surplus or shortage of the charged energy in charging the battery.